1. Field of the Invention
The present invention relates to a mold clamping device used in an injection molding machine and, in particular, to a mold clamping device which is free of play (backlash) in a mold-clamping-force transmitting system and which is appropriate for high-accuracy injection molding, which requires accurate position control of a mold, such as injection compression molding and core-back molding in which foaming is conducted under reduced pressure.
Priority is claimed on Japanese Patent Application No. 2007-311542 filed on Nov. 30, 2007, the content of which is incorporated herein by reference.
2. Description of the Related Art
A summary disclosed in Patent Document 1 as a mold clamping device used in a conventional injection molding machine will be described with reference to FIG. 10, and states (a) and (b) in FIG. 11. This mold clamping device is provided with: a fixed platen 10 which is installed securely on a machine base 1, has a mold clamping cylinder 3, and retains a fixed mold 30a; a movable platen 20 which is placed on the machine base 1, and is moved back and forth with respect to the fixed platen 10 by a mold opening/closing cylinder 2 so that a movable mold 30b retained thereby can be fit into or detached from the fixed mold 30a; a plurality of tie bars 7, each of which is coupled at one end with a piston 5 of the mold clamping cylinder 3, is equipped with a screw portion or a ring groove portion 8 at the other end part or the central part in the axial direction, penetrates through the movable platen 20 to arrive at a supporting plate 50, and is supported on the supporting plate 50; and half nuts 22 which are installed to the movable platen 20 and engaged with or disengaged from the screw portion or the ring groove portion 8 of the tie bar 7 (refer to FIG. 11).
The half nuts 22 are urged by a half-nut opening/closing cylinder 14, a piston 15, a piston rod 16 and others so that a first half nut 22a of the half nuts 22 is pulled and allowed to be in contact with a stopper 102, and an adjusting plate 100 is pushed out, thereby a second half nut 22b is pushed out by way of a connecting rod 101 fixed to the adjusting plate 100 and allowed to be in contact with a stopper 103 (refer to the state (a) in FIG. 11, disengagement state of the half nuts).
When the half-nut opening/closing cylinder 14 is urged in a reverse direction in the disengagement state of the half nuts, the piston 15, the piston rod 16 and others are urged in a pushing-out direction so that the first half nut 22a is press-fitted on and engaged with the screw portion or the ring groove portion 8 of the tie bar 7. The second half nut 22b is pulled in by way of the adjusting plate 100 and the connecting rod 101 due to this press-fitting force, and is engaged with the screw portion or the ring groove portion 8 of the tie bar 7 in such a manner that the first half nut 22a and the second half nut 22b embrace the screw portion or the ring groove portion 8 (refer to the state (b) in FIG. 11, engagement state of the half nuts).
A nut box 21 for guiding the half nuts 22 is installed securely at one end on the movable platen 20 and also provided at the other end on a mating-position adjustor 11 for the half nuts 22 and the screw portion or the ring groove portion 8 formed on the tie bar 7.
In the mold clamping device having the above-described constitution, there is provided a clearance between the half nuts 22 and the screw portion or the ring groove portion 8 formed on the tie bar 7 which is engaged with or disengaged from the half nuts 22 for their easy engagement or disengagement. Therefore, a clearance resulting from engagement of the half nuts 22 installed to the movable platen 20 with the screw portion or the ring groove portion 8 of the tie bar 7 entails play (backlash).
The technology for removing play (backlash) of a mold clamping device has been disclosed in Patent Document 2.
Specifically, the technology relates to a mold clamping device which is provided with a fixed platen, a movable platen which is arranged so as to oppose the fixed platen and allowed to move in an approaching/separating manner, a plurality of tie bars which are inserted into the movable platen to guide the movable platen so as to move in an approaching/separating manner with respect to the fixed platen, a mold opening/closing section which allows the movable platen to move smoothly in an approaching/separating manner with respect to the fixed platen, a section which compresses a mold, and a section which fixes the movable platen to the fixed platen by using a main cylinder on compression of the mold. In the mold clamping device, the fixing section is made up of an engagement groove provided at one of the movable platen and the fixed platen and a chuck member provided at the other of the movable platen and the fixed platen so as to be engaged with or disengaged from the engagement groove, thereby attaining fixation while removing backlash on engagement of the engagement groove with the chuck member.
In the mold clamping device, the section for compressing a mold is composed of a main cylinder installed at a site of the movable platen through which each of the tie bars is inserted, a piston rod having a predetermined length is inserted into the main cylinder, and the tie bar is inserted in a freely sliding manner into a hollow part formed in the piston rod along the axial direction. The fixing section is composed such that the engagement groove is provided on the piston rod of the main cylinder and the chuck member is provided on the fixed platen. The engagement groove and the chuck member are provided with side walls which are approximately orthogonal to the axial direction such that the side wall of the engagement groove and the side wall of the chuck member are opposed to each other. By allowing the side wall of the engagement groove and the side wall of the chuck member to be in contact with each other, fixation is attained while removing backlash on engagement of the engagement groove with the chuck member.
Further, in order to attain mutual contact between the side wall of the engagement groove and the side wall of the chuck member, there is provided with a cylinder and a piston rod for pressing and pulling the piston rod of the main cylinder having the engagement groove.
It is necessary to describe known technology of a mold clamping device disclosed in Patent Document 3.
The technology of Patent Document 3 is largely classified into: a center ram process in which a movable mold is directly compressed by way of a movable platen; and a plural mold clamping cylinder process in which mold clamping is performed by moving a movable platen by way of half nuts and a plurality of tie bars which are extended parts of pistons and piston rods fitted into a plurality of mold clamping cylinders. The technology related to the present invention is the latter, that is, the plural mold clamping cylinder process.
Patent Document 3 discloses a composite-type mold clamping device used in an injection molding machine which is provided with: a fixed platen to which a fixed mold is attached; a movable platen to which a movable mold is attached and which is arranged in opposition to the fixed platen and is freely moved back and forth with respect to the fixed platen by way of tie bars; a movement cylinder for allowing the movable platen to move back and forth on the tie bars; and an locking section which locks the movement of the movable platen at a predetermined position. The composite-type mold clamping device is further provided, as the locking section, with mold clamping half nuts disposed on an outer face of the movable platen and used for engagement of the tie bars with the movable platen, an opening/closing section for the mold clamping half nuts, high-pressure mold opening half nuts disposed so as to move freely on the tie bars and used for determining the engagement position of the mold clamping half nuts with the tie bars, an opening/closing section for the high-pressure mold opening half nuts, and a movement section for the high-pressure mold opening half nuts.
As the movement section for the high-pressure mold opening half nuts, there are described a mechanism in which a cylinder is attached to the fixed platen, thereby allowing the mold opening half nuts to move to any given position, and a mechanism in which a coupling bracket is attached to the movable platen and the bracket and the mold opening half nuts are guided so as to be engaged with each other by motions of the opening/closing section for the mold opening half nuts, thereby allowing the high-pressure mold opening half nuts to move to any given position by motions of the movable platen. In each of the above-described movement mechanisms, the mold clamping half nuts annexed on the opposite side across the movable platen can be reliably mated with an engagement part such as a screw or a groove formed on the tie bar, by adjusting the thickness of the movable platen and a position at which the mold clamping half nuts are attached.
In other words, according to the above-described constitution, when a mold is changed in thickness, the movement section for the mold opening half nuts adjusts the position of the mold opening half nuts by the amount of change in thickness of the mold, the opening/closing section for the mold opening half nuts is actuated so as to lock the mold opening half nuts, the movable platen is allowed to be in contact with the mold opening half nuts by actuation of the movement of the cylinder, and the mold clamping half nuts are closed. As a result, the mold clamping half nuts are reliably mated with the screw or the groove on the tie bar and the movable platen is securely locked on the tie bar.
As clearly described in Patent Document 3, an object of the technology described therein is to provide a composite mold clamping device used in an injection molding machine, etc., which is capable of making adjustment appropriately and easily when a mold is changed in thickness, and also capable of smoothly conducting mold closing and clamping operations which are complex operations, thereby attaining efficient injection molding, etc. However, this technology does not provide a mold clamping device which is free of play (backlash).
In other words, in order to remove backlash which naturally exists between the mold clamping half nuts attached on the movable platen and the screw or the groove of the tie bar when the mold clamping half nuts are mated with the screw or the groove of the tie bar, there is required an actuator which pushes the mold clamping half nuts to the opposite side of the mold opening half nuts, with the movable platen given as a supporting point, which is, however, not described at all in the above-described Patent Document.    [Patent Document 1] Japanese Patent No. 3524622 (FIG. 6 and FIG. 7)    [Patent Document 2] Japanese Unexamined Patent Application, First Publication No. H9-24520 (FIG. 1)    [Patent Document 3] Japanese Patent No. 3299140 (FIG. 3)